On the first day, he said he would take steps to “restore security and the constitutional rule of law.” One of the steps: “cancel every unconstitutional executive action, memorandum, and order issued by President [Barack] Obama.”

Trump also stated he would require that for every new federal regulation, two existing regulations must be eliminated; he will renegotiate NAFTA, or withdraw from the deal; he will withdraw from the Trans-Pacific Partnership; he will lift “Obama-Clinton roadblocks and allow vital energy infrastructure projects, like the Keystone Pipeline, to move forward.”

Josh Blackman, professor at Houston’s South Texas College of Law, says Trump will likely bring the Supreme Court back up to nine justices, then quickly clear cases from their docket.

“One of the most amazing parts of the Obama administration is how much has been accomplished by executive action,” Blackman says. “Whatever President Obama’s pen and phone giveth, Donald Trump’s Sharpie and Twitter can taketh away. And by the stroke of a pen, he can make a lot of these cases simply go away.”

In 2014, Obama issued executive actions allowing five million immigrants without legal U.S. documentation who are parents of citizens or lawful permanent residents to apply for work permits and safety from deportation.

“A Trump administration can simply withdraw that letter – in which case the Texas case goes away,” Blackman says. “There’ll be a serious shift in how the transgender bathroom cases proceed.”

There’s another case from Virginia regarding whether a high school student transitioning from female to male is permitted to use the boys’ bathroom. Blackman says the case could stick around or get sent back to a lower court.

Birth Control Coverage and the Affordable Care Act

In 2010, Obama signed the Affordable Care Act into law, mandating all citizens get health insurance coverage. What wasn’t included in the law was a mandate for insurance companies to cover birth control or contraceptives. But in May 2015, the Obama administration issued guidance to health insurers to cover 18 forms of contraception.

“There’s a very strong chance that the Trump administration will say ‘Okay religious charities … we’re simply going to exempt you from the mandate altogether,’” Blackman says. “Maybe the government will pay for women’s birth control, [or women] will get it through a different plan. … I think this is a likely way that this case can be resolved without the Supreme Court having to delve into these thorny issues of religious liberty once again.”

“It’s impossible to repeal the Affordable Care Act in its entirety through executive action,” Blackman says. “You would actually need a legislative vote to get rid of Obamacare. And this can be done, but the biggest hurdle will be the filibuster, and whether Democrats willing to filibuster the repeal.”

But Republicans could choose to bypass the filibuster or get rid of it altogether.

Clean Power Plan and the Environmental Protection Agency

Two dozen states, including Texas, and a coal mining company filed a lawsuit against the Environmental Protection Agency over an August 2015 Obama Administration mandate requiring states to cut carbon emission. The directive asked states to shift from coal to natural gas and renewable energy by 2030.

“We have this Clean Power Plan to impose vast restriction in how much CO2 we can emit,” Blackman says. “This is all done through executive action. … President Trump can simply withdraw the Clean Power Plan, undo the regulations issued by the EPA. … This is a consequence of not achieving enduring change through statute and the Clean Power Plan is basically gone.”